Monolithic perovskite–silicon tandem solar cells with MoO_x hole selective contact silicon bottom solar cells show a power conversion efficiency of 8%. A thin 15 nm-thick MoO_x contact to n-type Si was used instead of a standard p⁺ emitter to collect holes and the SiO_x/n⁺ poly-Si structure was deposited on the other side of the device for direct tunneling of electrons and this silicon bottom cell structure shows ~15% of power conversion efficiency. With this bottom carrier selective silicon cell, tin oxide, and subsequent perovskite structure were deposited to fabricate monolithic tandem solar cells. Monolithic tandem structure without ITO interlayer was also compared to confirm the role of MoO_x in tandem cells and this tandem structure shows the power conversion efficiency of 3.3%. This research has confirmed that the MoO_x layer simultaneously acts as a passivation layer and a hole collecting layer in this tandem structure.

In this work, nickel silicide was applied to tandem solar cells as an interlayer. By the process of thermal evaporation, a layer of NiO_x, hole transport layer (HTL) was deposited on n⁺ poly-Si layer directly. Nickel silicide was simultaneously formed by nickel diffusion from NiO_x to n⁺ poly-Si layer during the deposition and annealing process. The I–V characteristics of NiO_x/n⁺ poly-Si contact with nickel silicide showed ohmic contact and low contact resistivity. This structure is expected to be more advantageous for electrical connection between perovskite top cell and TOPCon bottom cell compared to the NiO_x/TCO/n⁺ poly-Si structure showing Schottky contact. Furthermore, nickel silicide and Ni-deficient NiO_x thin film formed by diffusion of nickel can improve the fill factor of the two sub cells. These results imply the potential of a NiO_x/nickel silicide/n⁺ poly-Si structure as a perovskite/silicon tandem solar cell interlayer.